1. Field of the Invention
The present invention relates to a reciprocating compressor, and more particularly, to an apparatus and method for controlling operations of a reciprocating compressor.
2. Description of the Background Art
In general, a reciprocating compressor compresses a refrigerant circulating at the interior of a cooling unit to a high temperature and high pressure as a piston moves linearly and reciprocally inside a cylinder. The reciprocating compressor can be divided into a recipro type and a linear type depending on how the piston is driven.
In the recipro type reciprocating compressor,. a crank shaft is coupled to a rotating motor and a piston is coupled to the crank shaft, whereby the piston is linearly and reciprocally moved by using a rotational force of the rotating motor.
In the linear type reciprocating compressor, the piston is directly connected to a linear motor, whereby the piston is linearly and reciprocally moved by using the linear motion of the linear motor.
Since the linear type reciprocating compressor does not need the crank shaft for converting the rotational motion to the linear motion, it has a relatively less frictional loss and thus, high compression efficiency compared to a general compressor.
In addition, the linear type reciprocating compressor can control a compression ratio by controlling a voltage applied to a motor, it can control a freezing capacity of a cooling unit.
An apparatus for controlling operations of the reciprocating compressor will now be described with reference to FIG. 1.
FIG. 1 is a block diagram showing the construction of an apparatus for controlling operations of the conventional reciprocating compressor.
As shown in FIG. 1, the apparatus for controlling operations of the reciprocating compressor includes: a voltage detector 15 for detecting a voltage applied to a motor of the compressor; a current detector 14 for detecting a current applied to the motor of the compressor; a stroke estimator 16 for estimating a stroke on the basis of the detected current, the detected voltage and parameters for the motor; a comparator 11 for comparing the stroke estimate value with a stroke reference value and outputting a difference signal according to the comparison result; and a controller 12 for controlling a stroke of the motor by varying a voltage applied to the motor on the basis of the outputted difference signal.
A method for controlling operations of the reciprocating compressor in accordance with the conventional art will now be described with reference to FIG. 2.
FIG. 2 is a flow chart of the method for controlling operations of the reciprocating compressor in accordance with the conventional art.
As shown in FIG. 2, the method for controlling operations of the reciprocating compressor includes: detecting values of voltage and current applied to the motor of the compressor (step S21); calculating an stroke estimate value on the basis of the detected voltage value, the detected current value and motor parameters (step S22); comparing the calculated stroke estimate value and a stroke reference value (step S23); reducing a voltage applied to the motor if the stroke estimate value is greater than the stroke reference value; and increasing a voltage applied to the motor if the stroke estimate value is smaller than the stroke reference value (step S25).
The method for controlling operations of the reciprocating compressor will be described in detail as follows.
First, the voltage detector 15 detects a value of a voltage applied to the motor of the compressor at every predetermined period, and outputs the detected voltage value to the stroke estimator 16. The current detector 14 detects a value of a current applied to the motor of the compressor and outputs the detected current value to the stroke estimator 16 (step S21).
The stroke estimator 16 applies the detected current value, the detected voltage value and the motor parameters (e.g., a resistance or an inductance of the motor) to equation (1) shown below, to calculate a stroke estimate value, and output the calculated stroke estimate value to the comparator 11 (step S22).
                    x        =                              1            α                    ⁢                      ∫                                          [                                                      V                    M                                    -                                      R                    ⁢                                                                                  ⁢                    ⅈ                                    -                                      L                    ⁢                                                                                  ⁢                    ⅈ                                                  ]                            ⁢                              ⅆ                t                                                                        (        1        )            
Wherein, α is a motor constant, VM is a voltage of the motor, ‘R’ is a resistance of the motor, ‘L’ is an inductance of the motor, and ‘i’ is a current of the motor.
The comparator 11 compares the outputted stroke estimate value with the stroke reference value, generates a difference signal according to comparison, and outputs the generated difference signal to the controller 12 (step S23).
The controller 12 controls the stroke of the compressor by varying the voltage applied to the motor on the basis of the inputted difference signal. In this case, if the stroke estimate value is greater than the stroke reference value, the controller reduces the voltage applied to the motor (step S24). If the stroke estimate value is smaller than the stroke reference value, the controller 12 increases the voltage applied to the motor (step S25).
In this manner, the apparatus for controlling operations of the conventional reciprocating compressor stably drives the compressor by controlling the stroke uniformly by varying the voltage applied to the motor.
However, the conventional apparatus for controlling operations of the reciprocating compressor has the following problem.
That is, since the stroke of the compressor is estimated on the basis of the motor parameters such as the motor constant, the motor resistance, the motor inductance and motor current, deflections of the motor parameters causes an error in the estimated stroke of the compressor.